• A fixed length record is one where the length of the fields in each record has been set to be a certain maximum number of characters long.

• A set amount of storage space is set aside for each field. If the contents of a field don’t fill the space completely it is remains empty and is wasted.

The problems with fixed length records are:-

• Fields very rarely contains the maximum number of characters allowed which wastes space;
• Values sometimes can’t be entered because they are too large to fit inside the allowed space in a field.

The advantage of fixed length records is that they make file processing much easier because the start and end of each record is always a fixed number of characters apart. This makes it much easier to locate both individual records and fields.

A variable length record is one where the length of a field can change to allow data of any size to fit.

• A special marker (# in this example) indicates where each field ends.
• The length of a field depends upon the data that is placed in it. Only the space needed for a field is ever used — so none is wasted.
• The advantage of variable length records is that space is not wasted, only the space needed is ever used.
• The main problem with variable length records is that it is much more difficult to locate the start and end of individual records and fields.
• To separate variable length records each field has a special character to mark where it ends — called an ‘end-of-field marker’. When records need to be located the computer must count through the end-of-field markers to locate individual records and fields.

• File operations are the different things that can be done to a computer file.
• The main types of file operation are searching, sorting, updating and merging.

Searching

• Searching, or interrogating a file, involves looking for an individual record or group of records that match a certain condition.
• Searches are also called queries.
• To search a database the user must enter a query. The query tells the software which fields to look at in each record and what to look for.

Sorting

• Sorting involves putting the records in a file into a particular order, such as alphabetical order.

Merging

• Merging involves combining two files to produce one new file. This can be done by merging a file of new records to be added with another file that contains all of the existing records — called the master file.

Updating

• The information stored in computer files must be kept up-to-date or it will cause problems for the business or organisation that’s using it.
• To keep a file up-to-date it must be regularly updated. This involves inserting, deleting and amending records.
• When a new record needs to be added to a file, it is inserted. Records are deleted when they are no longer needed. Records are amended when the data in one or more of the fields needs to be altered for some reason.
• Details of all the changes that need to be made to a master file are often collected together in a transaction file.
• The master file is updated by comparing it with the transaction file and making changes to any records that appear in both files. Normally at least three ‘generations’ of a master file are kept for backup purposes. If the latest version of the master file is damaged it can be recreated by re-running the previous update using the old master and transaction files.
• The grandfather-father-son method of updating can be seen below.